Single-gun,plural-beam cathode ray tube having all beams focused by the passage thereof through the optical center of a common electron lens



Dec. 8, 1970 susu os m ETAL 3,546,516

SINGLE-GUN, PLURAL-BEAM cATHoDE RAY TUBE HAVING ALL BEAMS FOCUSED BY THE PASSAGE THEREOF THROUGH THE OPTICAL CENTER OF A COMMON ELECTRON LENS Filed June 2, 1969 M 1.1 E 1 N i I r i I i I? I 2 \E l Q) I l f 13. m

J & E a i INVENTORS \& SUSUMU YOSHIDA AKIO OHGOSHI SENRI MIYAOKA YOSHIHARU KATAGIRI ZQMM United States Patent US. Cl. 313--69 5 Claims ABSTRACT OF THE DISCLOSURE A single gun plural cathode ray tube having a plurality of grids at varying potentials in which an electrostatic focusing lens is provided for focusing on an electron receiving screen all of the beams passed thereto from the cathodes and associated grids, and the plural beams are made to cross each other at the optical center of the lens for minimizing aberrations of the beam thereby, a grid is provided between the electrostatic focusing lens and the associated grids which is at ground potential to eliminate the deleterious effects of intergrid interference. The provided grid also has enlarged electron beam receiving apertures therein in relation to the associated grids which are adjacent thereto to facilitate the placement of the apertures in the provided grid in the path of the electron beam thereby obviating the need for close tolerances.

This invention relates generally to improvements in cathode ray tubes of the type, as particularly disclosed in US. Pat. No. 3,448,316 which issued on June 3, 1969, in which a single electron gun is provided for emitting a plurality of electron beams to produce a color picture, for example, as in color television receivers. It should be understood, however, that the teachings of this invention are applicable to plural guns for color and to black and White receivers also.

This application is a continuation-in-part application of co-pending patent application Ser. No. 697,414, filed June 12, 1968, and entitled, Cathode Ray Tube which issued on June 3, 1969 as US. Pat. No. 3,448,316.

In the development of electron guns for cathode ray tubes especially in the field of color television, there are two basic systems. In the conventional system three independent electron guns are utilized which emit electron beams. These beams are modulated by corresponding color signals and acted upon by a grid system so as to be focused on a collector or electron receiving screen which may be simply a phosphor or luminescent screen with a perforated electrode or shadow mask located adjacent thereto. It has been found that using three independent electron guns to produce the beams is costly and by reason of the space required for the three guns, the available flexibility for miniaturizing the tube is limited.

To avoid the latter disadvantages, it has been proposed to provide a color picture tube of the single-gun, plural beam type in which a single electron gun emits three beams from either three respective cathodes or a single cathode. The plural beams can then be passed through a lens-like focusing system, so as to converge at the electron receiving screen.

In both systems the cathodes are each housed within a grid having an aperture therein and this grid is at a potential with respect to the cathode. One or more additional grids, having apertures therein for the reception of electrons, and also having a desired potential applied thereto are used to accelerate the beam and properly converge it on the electron receiving screen. The grids are spaced from each other axially and radially in a cathode ray tube generally in the neck portion of the tube. The electric fields emitted by the bias placed on the grids can affect another grid which is within its field if it is not spaced far enough from the field. Unfortunately, the amount of space available in the neck of a cathode ray tube does not permit a wide latitude in spacing, and the strength of the field is important as it relates to the grid from which the electron beams are to be properly attracted. Therefore, when two or more grids must be necessarily close together for proper operation, the deleterious effects of intergrid interference are present, and a distorted picture on the electron beamreceiving screen can result.

To eliminate these deleterious effects, it has been found that by maintaining an intermediate grid at ground potential, it functions as a shield which protects one grid from stray electric fields caused by adjacent grids.

It is also known that prior art grids use an aperture therein for the reception of the electron beams. The apertures are very small and must be carefully aligned with the beam emitted from a cathode or the beam will deflect from the grid and a distorted picture will appear on the screen, if 'indeed it appears at all. As a result of this, elaborate jigs and fixtures had to be devised to insure the precise placement of the grids. Even with the latter expensive jigs and fixtures, an inordinate amount of assembly time had to be spent in grid alignment because the placement is so critical.

To overcome this disadvantage, applicants devised an improved grid system which does not utilize the uniform size aperture commonly employed in the prior art. It has been found that by making the size of the openings of one grid larger with respect to the other that the critical placement of one grid with respect to the other has been eliminated. This is true because a larger area is available through which the beam can pass and a slight misplacement or movement of a grid will not distort the emitted beam because it can still pass through the larger grid opening.

In the following detailed description of an illustrative embodiment, particular reference is made to a single-gun, plural-beam system which is used in color picture tubes, but it is to be understood that the described single-gun, plural-beam system according to this invention can be applied to any other gun used in a plural beam cathode ray tube or in any electronic devices using a grid or electrode system-to accelerate an electron beam.

The above features and advantages of this invention Will become apparent from the following detailed description of an illustrative embodiment which is to be read in conjunction with the accompanying drawings, in which:

The figure is a schematic longitudinal sectional view showing a plurality of cathodes and grids in an improved plural beam electron gun.

Referring to the figure there is shown a plurality of cathodes 10, 11 and 12, having respective electron-emitting surfaces, which are arcuately arranged in a horizontal plane the surfaces being arranged so that perpendiculars thereto converge and extend through the optical center F of the lens. The cathodes are so arranged so as to eliminate the necessity of an auxiliary lens to converge the emitted beams which is more fully discussed in co-pending application Ser. No. 697,414, filed Jan. 12, 1968, and entitled Cathode 'Ray Tube, which issued on June 13, 1969 as US. Pat. No. 3,448,316. Each cathode has a respective grid 13, 14 and 15 having a potential applied thereto, which can surround the cathode and has an aperture 16 located approximately in the center of the face of the grid enabling it to function as a window for an emitted beam B B and B from the respective cathodes. The apertured faces or end walls of the grid 13, 14 and 15 are parallel to and equidistantly adjacent to the respective electron-emitting surfaces of the respective cathodes 10, 11 and 12.

A grid 17 having an arcuate face 18 thereon has a plurality of apertures 21 therein each of which receives a respective electron beam. An electrical potential of suitable value is impressed on the grid 17 thereby causing the emitted electrons to converge substantially at an optical center F of a focusing lens L. Additional grids 19 and 20 can be used to produce the desired effects on the emitted electron beams. The grids can be in the form of an enclosure which is open at one end thereof or open at both ends. These grids 17, 19 and 20 comprise an electrostatic focusing lens, and, as disclosed in my previously referred to copending application, now US. Pat. No. 3,448,316, grids 17 and 20 may be at a high potential while grid 19 may be at a low potential.

The aforementioned cathodes and grids are located in the neck of a cathode ray tube which is a relatively small space. It is desirable to make the neck as small as possible especially if the cathode ray tube is to be inserted in a miniature television cabinet. In order to reduce the length of the neck of the tube, it is necessary that the grids 13, 14, 15 and 17 be brought into close proximity. The electric field which radiates from the grid 17 can thereby affect each grid 13, 14 and 15 in a different manner because of the arcuate arrangement of the grids. For example, the distance from the face of the grid 13 to the point where the emitted beam enters the aperture 21 on the face of the grid 17 is greater than the distance between the face of the grid 14 to the corresponding aperture 21 on grid 17. Since the strength of the electric field at a particular point is a function of distance, the effect on an electron at the face of grid 13 and at the face of grid 14 will be different. The emitted beams will, therefore, be distorted and an undesirable picture can result. To overcome this problem a grid 22, which may be cup-shaped as shown in the figure, is mounted between the grids 13, 14, 15 and 17 preferably close to the cathodes. This grid 22 may have an end wall, portions of which are equidistant from and substantially parallel to the apertured faces of the grids 13, 14 and 15, and these end wall portions may be surfaces of revolution such as may be present when the end wall is an arcuate surface concentric with the arcuate surface to which the apertured faces of the grids 13, 14 and 15 are tangent. The grid 22 has a plurality of apertures 23 therein which are aligned with the respective apertures 16 in the grids 13, 14 and 15 and which may be larger than these apertures 16. It has been found that if the apertures 23 are approximately twice the size of the apertures 16 that the beneficial results of the invention can be achieved. This will be more fully discussed below.

The grid 22 is at ground potential whereby it functions somewhat as a shield for the grids 13, 14 and 15. The effect of placing the grid 22 adjacent the cathode grids 13, 14 and 15 is to effectively apply the same strength electric field to the cathode grids despite their varying distances from the grid 17.

As pointed out above the apertures 23 in the grid 22, which is at ground potential, are approximately two or more times the size of the apertures 16 in the cathode grids 13, 14 and 15. It is obvious that the electron beams B B and B emanating from the respective cathodes 10, 11 and 12 must enter the apertures 23 in the face of the grid 22. Since the size of the openings in the grid 22 are much larger than the openings 16 in the cathode grids 10, 11 and 12, the criticality of locating the openings in the grid 22 in line With the beams from the cathodes 10, 11 and 12 is greatly diminished. If the grid 22 is not perfectly placed in relation to the cathode grids 10, 11 and 12 the beams B B and B will still pass through the openings 23 in the grid 22 because they now have a larger area into which they can pass.

While they has been shown and described a single embodiment of the invention, it will be obvious to those skilled in the art that changes and modifications may be 'made without departing from the invention, and that it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A single-gun, plural-beam cathode ray tube comprising an electron-receiving screen, a plurality of spaced cathodes for generating respective beams and having electron emitting surfaces arranged so that perpendiculars thereto converge and cross each other at a point in said tube intermediate said cathodes and said screen with said electron emitting surfaces being substantially equidistant from said point, electrostatic focusing lens means common to all of said beams to focus the latter on said screen, said lens means having an optical center and being located to dispose said optical center substantially at said point, first control grids respectively associated with said cathodes and including end walls parallel and equidistantly adjacent to said electron emitting surfaces of the respective cathodes, said end walls of the first control grids having apertures for the passage therethrough of the respective beams, and a common second grid interposed between and spaced from said first control grids and said electrostatic focusing lens means, said second grid being cup-shaped and including an end wall, portions of which are equidistant from, and substantially parallel to said end walls of the first control grids, said portions of the end wall of said second grid having apertures therein substantially aligned with respective apertures of said first control grids, said electrostatic focusing lens means including a grid to which a high potential is applied and which is disposed adjacent said second grid in axially spaced relation thereto, and said second grid being grounded to prevent electrical discharges between said high potential grid of the lens means and said first control grids.

2. A cathode ray tube according to claim 1, in which said apertures of the second grid are substantially larger than said apertures of the first control grid to ensure free passage of said beams through said apertures of the second grid even when the apertures of said first and second grids are imprecisely aligned.

3. A cathode ray tube according to claim 2, in which said apertures of the second grid are at least twice as large as the respective apertures in said first grids.

4. A cathode ray tube according to claim 1, in which said end wall portions of the second grid are parts of a surface of revolution.

5. A cathode ray tube according to claim 1, in which said end wall portions of the second grid are parts of an arcuate surface having its center of curvature at said point, and said end walls of the first control grids are tangent to an arc concentric with said arcuate surface of the second grid.

References Cited UNITED STATES PATENTS 2,887,598 5/1959 Benway 3l370 JAMES W. LAWRENCE, Primary Examiner V. LAERANCHI, Assistant Examiner US. Cl. XJR. 315-13 

